Two commonly employed electrostatographic copying and printing processes are the electrophotographic or xerographic process and the dielectric or electrographic process. In the electrophotographic process an electrostatic image is formed on a photoconductive insulating surface by charging the surface and exposing it to an image of light and shadow to be recorded, whereupon the electric charge is dissipated in the light areas. The image is then developed by applying pigment material to the image-bearing surface. Depending upon the nature of the process, the developed image is then either fixed on the original photoconducting surface or transferred to a final image support member and fixed.
In the dielectric process an electrostatic image is applied to a conductive image support member coated with an insulating dielectric layer. The image pattern is generated by way of an electrically energized stylus or an electrostatic writing tube (commonly referred to as a CRT pin-tube) which is in close proximity to the dielectric layer. Energizing of the stylus or the electrostatic writing tube results in the deposition of a charge pattern on the surface of the dielectric layer, commonly referred to as a latent image. The latent image is developed by depositing pigment materials onto the image-bearing surface and the developed image is fixed by bonding the pigment materials to the surface.
A xerographic developing material comprising an encapsulated color-forming composition within a shell having surface triboelectric properties suitable for electrostatic deposition is disclosed in U.S. Pat. No. 3,080,251. The said color-forming composition can comprise basic chromogenic lactone compounds. The color-forming composition, released by means of pressure, reacts with an acidic adsorbent photoconductive material which is required.
An electrophotographic method which comprises developing a latent image formed on a photosensitive member comprising a photoconductive material and a color-forming agent (B) with a toner comprising a color-forming agent (A) is disclosed in U.S. Pat. Nos. 3,879,196, 3,880,656, 4,054,712 and 4,148,968. Phenolic materials are disclosed as examples of color-forming agents (A) and basic chromogenic lactone compounds are disclosed as examples of color-forming agents (B). The disclosure contemplates only electrophotographic processes; dielectric processes are neither disclosed or suggested.
In all of the above-disclosed processes, only one of the color-forming agents resides in the final image support member. The other component of the color-forming reactant pair is contained within the toner material.
Heat-sensitive mark-forming systems, wherein both components of the color-forming reaction are contained within the color-forming layer, have been disclosed in U.S. Pat. No. 3,539,375. When the reactive components of such heat-sensitive mark-forming systems are incorporated into a reactive dielectric record material, a dark, prematurely colored product results.
Pressure-sensitive mark-forming systems, wherein both components of the color-forming reaction are contained within the color-forming layer, have been disclosed in U.S. Pat. No. 4,197,346. These pressure-sensitive mark-forming systems, wherein both color-forming components reside within a single color-forming layer, are called self-contained systems. In these prior art self-contained systems, colored images are formed as a result of the intermixing of the color-forming components as a consequence of microcapsule rupture brought about by the application of writing or impact pressures.
Thermochromic material exhibiting reversible metachromism and comprising (A) an electro-donating chromatic organic component, (B) a compound having a phenolic hydroxyl group, (C) higher aliphatic monovalent alcohols and (D) higher monovalent acid alcohol esters is disclosed in U.S. Pat. No. 4,028,118. The chromatic organic compound can include crystal violet lactone and the phenolic compound can include phenolphthalein.